1. Field of the Invention
The present invention relates to a method of stopping machining operation in a grinding machine or the like and a machining controlling apparatus therefor.
2. Description of the Related Art
Recently, a grinding machine has a control system including a numerical control unit, and performs numerical control for high-precision machining of a workpiece. Specifically, the workpiece is ground by a grinding wheel while relatively moving the rotating grinding wheel with respect to the workpiece along a numerically controlled locus. However, in a conventional grinding machine having the numerical control unit, when a pin portion or the like of, for example, a camshaft or a crankshaft is ground while a journal thereof serves as a rotating shaft, such grinding requires to forwardly or backwardly move a wheel spindle stock with respect to the workpiece. For this reason, when a power failure has occurred, unless the timing when a spindle apparatus for rotatively driving the workpiece is stopped and the timing when the wheel spindle stock for forwardly or backwardly moving the grinding wheel is stopped coincide with each other, there is the possibility that the grinding wheel bumps into the workpiece, thereby causing damage to the workpiece or the machine. Therefore, such a grinding machine stops through a simple dynamic brake circuit interlocking with cutoff of power supply by means of a relay, or provides an uninterruptive power supply unit as a countermeasure against a power failure. At the time of a power failure, a dynamic brake is applied to a motor for rotatively driving the spindle apparatus by the numerical control unit whose power supply is backed up by the uninterruptive power supply unit, while mechanical driving portions other than the motor for rotatively driving the spindle apparatus are rapidly stopped by the use of regenerative resistance or mechanical brakes.
However, the uninterruptive power supply unit not only is expensive but also makes the equipment large.
Accordingly, the object of the invention is to provide a method of stopping machining operation in an apparatus having a tool for performing machining with respect to a workpiece in contact therewith, such as a grinding machine, for retreating the tool from the workpiece at the time of power failure without causing damage to the machine and the workpiece and without requiring an uninterruptive power supply unit which requires a large equipment in a controller, as well as a machining controlling apparatus.
To attain the above object, according to a first aspect of the invention, there is provided a method of stopping a machining operation of a machining tool, wherein the machining operation of the machine tool performed by synchronously driving a rotating workpiece held by a spindle apparatus and a reciprocating tool is controlled in accordance with machining profile data stored in a controlling apparatus, the method comprising the steps of:
preparing, in the controlling apparatus, a power-supply-drop detecting unit detecting a power failure or a drop in power supply supplied to the control unit and a tool-retreating-formula storing unit storing data based on a tool retreating formula for retreating the tool from the workpiece;
decelerating the spindle apparatus and adding the data based on the tool retreating formula into the machining profile data, when the power failure or the drop in power supply is detected; and
retreating the tool from the workpiece in synchronous with the rotation of the spindle apparatus based on the added machining profile data within a period until the controlling operation by the controlling apparatus becomes impossible, whereby the machining tool is stopped after retreating the tool from the workpiece.
By adopting the above-described method of stopping the machining operation, when the power failure or the drop in power supply has been detected by the power-supply-drop detecting unit, the data based on the tool retreating formula is added to the machining profile data, and
the tool is retreated from the workpiece within a period until the controlling operation by the controlling apparatus becomes impossible due to the drop in power supply, and the machine tool is subsequently stopped. Accordingly, even if a power failure has occurred, it is possible to prevent causing damage to the workpiece or the machine tool. For this reason, an uninterruptive power supply unit which has hitherto been required becomes unnecessary.
Further, according to a second aspect of the invention, there is provided a method of stopping a machining operation of a machining tool, wherein the machining operation of the machine tool performed by synchronously driving a rotating workpiece held by a spindle apparatus and a reciprocating tool is controlled in accordance with machining profile data stored in a controlling apparatus, the method comprising the steps of:
preparing, in the controlling apparatus, an input unit inputting an apparatus stop instruction for stopping the machining operation and a tool-retreating-formula storing unit storing data based on a tool retreating formula for retreating the tool from the workpiece;
decelerating the spindle apparatus and adding the data based on the tool retreating formula into the machining profile data, when the apparatus stop instruction is inputted; and
retreating the tool from the workpiece in synchronous with the rotation of the spindle apparatus based on the added machining profile data within a period of time until the controlling operation by the controlling apparatus becomes impossible, whereby the machining tool is stopped after retreating the tool from the workpiece.
By adopting the above-described method of stopping the machining operation, when the apparatus stop instruction has been inputted, the control unit adds the data based on the tool retreating formula to the machining profile data, the tool is retreated from the workpiece within a predetermined period, and the machine tool subsequently stops. Accordingly, even if an instruction for such as an emergency stop or the like is inputted, the tool moves away from the workpiece smoothly and speedily and stops in such a manner as to be spaced apart from the workpiece, so that the machine tool can be stopped rapidly without causing damage to the workpiece or the machine tool.
In addition, according to a third aspect of the invention, in the method of the first and second aspects, the data based on the tool retreating formula to be added into the machining profile data is data for accelerating or decelerating a feeding speed of the tool with respect to the workpiece within a predetermined period.
By adopting the above-described method of stopping the machining operation, as the data based on the tool retreating formula is added to the machining profile data, when a power failure or a drop in power supply has been detected, or when the apparatus stop instruction has been inputted, the retreating speed of the tool gradually changes. As a result, a sudden speed change does not occur at the time of the disengagement of the tool engaged in machining, thereby making it possible to prevent causing damage to the apparatus.
Moreover, according to a fourth aspect of the invention, there is provided a machining controlling apparatus comprising:
a control unit controlling, in accordance with machining profile data, the machining operation of a machine tool performed by synchronously driving a rotating workpiece held in a spindle apparatus and a reciprocating tool;
a power-supply-drop detecting unit detecting a power failure or a drop in power supply supplied to the control unit; and
a tool-retreating-formula storing unit storing data based on a tool retreating formula for retreating the tool from the workpiece,
wherein when the power failure or the drop in power supply has been detected by the power-supply-drop detecting means, the control unit decelerates the spindle apparatus and adds the data based on the tool retreating formula to the machining profile data, and stops the machine tool after the tool is retreated from the workpiece in synchronous with the rotation of the spindle apparatus based on the added machining profile data within a period until the controlling operation by the control unit becomes impossible.
By adopting the above-described apparatus, the machining operation of the machine tool is controlled by the control unit in accordance with the machining profile data. Here, when the power failure or the drop in power supply provided to the control unit has been detected by the power-supply-drop detecting unit, the data based on the tool retreating formula is added to the machining profile data, and the tool is retreated from the workpiece under control by the control unit within a short time until the controlling operation by the control unit becomes impossible due to the drop in power supply. After the tool has been retreated, the machine tool is stopped. Accordingly, even if the uninterruptive power supply unit is not provided, it is possible to stop the tool away from the workpiece, thereby making it possible to prevent causing damage to the workpiece or the machine tool.
Further, according to a fifth aspect of the invention, there is provided a machining controlling apparatus comprising:
a control unit controlling, in accordance with machining profile data, the machining operation of a machine tool performed by synchronously driving a rotating workpiece held in a spindle apparatus and a reciprocating tool;
an input unit inputting an apparatus stop instruction for stopping the machining operation; and
a tool-retreating-formula storing unit storing data based on a tool retreating formula for retreating the tool from the workpiece,
wherein when the apparatus stop instruction has been inputted, the control unit decelerates the spindle apparatus and adds the data based on the tool retreating formula to the machining profile data, and stops the machine tool after the tool is retreated from the workpiece in synchronous with the rotation of the spindle apparatus based on the added machining profile data within a predetermined period until the controlling operation by the control unit becomes impossible.
By adopting the above-described apparatus, the machining operation of the machine tool is controlled by the control unit in accordance with the machining profile data. Here, when the apparatus stop instruction is inputted by the input unit, the data based on the tool retreating formula is added to the machining profile data, the tool is retreated from the workpiece within a very short time, and the machine tool is stopped after the tool has been retreated. Accordingly, even if the uninterruptive power supply unit is not provided, it is possible to stop the tool away from the workpiece at the time of, for instance, an emergency stop, thereby making it possible to prevent causing damage to the workpiece or the machine tool.
Additionally, according to a sixth aspect of the invention, in the apparatus of the fourth and fifth aspects, the data based on the tool retreating formula to be added into the machining profile data is data for accelerating or decelerating a feeding speed of the tool with respect to the workpiece within a predetermined time.
By adopting the above-described arrangement, when a power failure or a drop in power supply has been detected, or when the apparatus stop instruction has been inputted, the relative speed of the tool with respect to the workpiece gradually changes. As a result, a sudden speed change does not occur, and it is possible to prevent the occurrence of a shock entailed by the speed change, thereby making it possible to prevent causing damage to the apparatus.